The present invention relates to novel pharmaceutical compounds useful as selective antagonists of the A2B adenosine receptor. Furthermore, the present invention relates to novel pharmaceutical compositions useful for treating certain indications including asthma and diarrhea. The present invention also relates to novel methods of treating certain indications including asthma and diarrhea.
There is substantial evidence that adenosine modulates many physiological processes. Its actions are mediated by interaction with specific cell membrane receptors. Four types of adenosine receptors have been identified: A1, A2A, A2B and A3. All four subtypes have been cloned from human tissue. Adenosine receptors have the seven transmembrane domain structure typical of G protein-coupled receptors. Adenosine receptors are widely distributed throughout the body and are probably present in every cell.
Adenosine receptors were initially classified by the ability to inhibit (A1) or activate (A2 and A2B) adenylate cyclase. A3 receptors also inhibit adenylate cyclase. Modulation of adenylate cyclase is mediated through coupling to Gs and Gi guanine-nucleotide regulatory proteins. It is now known that adenosine receptors are also coupled to other intracellular signaling pathways. A1 and A3 receptors, for example, can couple to phospholipase C; A1 receptors are also coupled to K channels. A2B receptors are also coupled to Gq and mediate activation of PLC, Ras and MAP kinases.
Substituted xanthines represent the most potent class of adenosine-receptor antagonists reported to date. See Katsushima et al., Structure-Activity Relationships of 8-cycloalkyl-1,3-dipropylxanthines as Antagonists of Adenosine Receptors, J. Med. Chem., 33:1906-1910 (1990); and Martinson et al., Potent Adenosine Receptor Antagonists that are Selective for the A1 Receptor Subtype, Molecular Pharmacology, 31:247-252 (1987).
The study of A2B receptors has been hampered by the lack of selective pharmacological probes. Nonetheless, A2B receptors can be distinguished from A2A receptors by their low affinity and their distinct rank order of potency for agonists. NECA (5xe2x80x2-N-ethylcarboxamidoadenosine) is one of the most potent agonist at A2B receptors, but is also effective at A2A receptors. On the other hand, the agonist CGS 21680 (4-((N-ethyl-5xe2x80x2carbamoyladenos-2-yl)-aminoethyl)-phenylpropionic acid) is virtually inactive at A2B receptors, whereas it is as potent as NECA at A2A receptors. The lack of effectiveness of CGS 21680 has proven useful in the functional characterization of A2B receptors. A2B receptors also have a very low affinity to the A3 selective agonists IB-MECA and N6-benzyl NECA. These agonists can, therefore, be used to differentiate between A2B and A3 receptors. In summary, A2B receptors can be identified by their unique rank order of potency for agonists NECA greater than PIAxe2x89xa7IB-MECA greater than CGS-21680.
Whereas A2B receptors have, in general, a lower affinity for agonists compared to other receptors subtypes, this is not true for antagonists. The structure activity relationship of adenosine antagonists on A2B receptors has not been fully characterized, but at least some xanthines are as or more potent antagonists of A2B receptor subtypes than of other subtypes. In particular, DPSPX (1,3-dipropyl-8-sulphophenylxanthine), DPCPX and DPX (1,3 diethyl-phenylxanthine) have affinities in the mid to high nM range.
The present inventors have recognized that A2B receptors modulate important physiological processes. As stated by Feoktistov et al., Adenosine A2B Receptors as Therapeutic Targets, Drug Dev Res 45:198; A2B receptors have been implicated in mast cell activation, asthma, vasodialation, regulation of cell growth, intestinal function, and modulation of neurosecretion. Also see Feoktistov et al. Trends Pharmacol Sci 19:148-153.
Methods of mast cell activation, treating and/or preventing asthma and vasodialation, regulation of cell growth and intestinal function, and modulation of neurosecretion are all objects of the present invention.
As stated above, A2B receptors modulate important physiological processes. For example, A2B receptors are found in the colon in the basolateral domains of intestinal epithelial cells, and increase chloride secretion. Selective A2B antagonists with poor gastrointestinal absorption can also be useful in blocking intestinal chloride secretion. Thus, it is an object of the present invention to prevent and/or treat inflammatory gastrointestinal tract disorders including diarrhea.
Additionally, there are vascular beds in which NECA produces profound vasodilation. Based on reasonable confirmation that A2B receptors mediate vasodilation in the pulmonary circulation, an object of the present invention is to prevent and/or treat cardiac diseases.
A2B receptors are also present in cultured vascular smooth muscle cells and have been found to inhibit their growth. Since impaired adenosine mechanisms may play a role in the vascular remodeling process observed in atherosclerosis and hypertension, an object of the present invention is to prevent and/or treat atherosclerosis and hypertension.
A2B receptors are also present in endothelial cells and have been found to stimulate their growth. Since this will lead to growth of new blood vessels (angiogenesis). An object of this invention is to prevent and/or treat diseases characterized by abnormal blood vessel growth, such as diabetic retinopathy and cancer.
There is evidence that A2B receptors modulate mast cell function and that A2B receptors are present in mouse bone marrow-derived mast cells. A2B receptors have been shown to produce direct activation of HMC-1 cells, a cell line with phenotypic characteristics of human lung mast cells. This process involved activation of PLC through Gq proteins, and activation of MAP kinasis, intracellular processes not previously described for A2 receptors. Virtually identical findings have been reported in a dog mastocytoma cells line. Evidence based on the research of the present inventors, using immunofluorescence techniques with a specific chicken anti-human A2B antibody, indicates the presence of A2B receptors in human lung mast cells obtained from asthmatics by bronchoalveolar lavage cells. Thus, an object of the present invention is to prevent and/or treat asthma. Asthma continues to be a substantial medical problem that affects approximately 5-7% of the population. Despite advances in its treatment, the prevalence of asthma emergency department visits, hospitalizations, and mortality related to the disease, all appear to be on the rise.
Additionally adenosine treatments such as inhaled adenosine provokes bronchoconstriction in asthmatics, but not in normals. This process involves mast cell activation because it is associated with the release of mast cell mediators, including histamine, PGD2-xcex2-hexosaminidase and tryptase, and because it can be blocked by specific histamine H1 blockers and chromolyn sodium. Furthermore, adenosine has been shown to potentiate activation of purified human lung mast cells. The low affinity of this process suggests the involvement of A2B receptors. Given that inhaled adenosine has no effect in normals, there appears to be an intrinsic difference in the way adenosine interacts with mast cells from asthmatics. The in vitro response produced by A2B receptors in HMC-1 cells and in dog mastocytoma cells appears to mimic in vivo responses to inhaled adenosine in asthmatics, inasmuch as adenosine provokes mast cells activation in these cell lines as it does in asthmatics. Thus, an object of the present invention is a method of modulating mast cell function or activation of human lung cells.
Theophylline remains an effective antiasthmatic agent even though it is a poor adenosine receptor antagonist. However, considerable plasma levels are needed for it to be effective. Additionally, Theophylline also has substantial side effects, most of which are due to its CNS action, which provide no beneficial effects in asthma, and to the fact that it non-specifically blocks all adenosine receptor subtypes. The side effect profile of theophylline, therefore, can be improved substantially by generating selective and potent A2B antagonists such as the compounds of the present invention.
It is known that adenosine exhibits neurotransmitter depressing activity, bronchospasmic activity, bone absorption promoting activity, and the like via an A2 receptor. Therefore, adenosine A2 receptor antagonists are expected as therapeutic agents for various kinds of diseases caused by hyperergasia of adenosine A2 receptors, for example, therapeutic agents for Parkinson""s disease, anti-dementia agents, antidepressants, anti-asthmatic agents, and therapeutic agents for osteoporosis. Thus, an object of the present invention is providing such a therapeutic agent.
U.S. Pat. Nos. 4,352,956 and 4,804,664 to Kjellin et al. disclose the antiasthmatic drug enprofylline. Enprofylline has been discovered to be a relatively selective A2B antagonists. Enprofylline is of the following formula: 
As is more fully described below, the compounds of the present invention have a potency much higher than enprofylline and are yet 40- to 60-fold selective compared to A2A and A1.
As stated above, U.S. Pat. Nos. 4,325,956 and 4,804,664 to Kjellin et al. disclose xanthine derivatives including enprofylline used for the treatment of cardiac disease and chronic obstructive airway disease.
U.S. Pat. No. 4,089,959 to Diamond discloses xanthine derivatives useful for treating bronchial asthma and other bronchospastic diseases. More specifically, the xanthine derivatives 1,3,8-trialkylxanthines. Diamond discloses that the introduction of an alkyl group in the 8-position of the xanthine nucleus has been discovered to produce a compound having long lasting activity.
U.S. Pat. No. 4,120,947 to Diamond discloses 1,3-dialkyl-7-carbomethoxytheophylline xanthine derivatives useful in treating bronchospastic and allergic diseases. U.S. Pat. No. 4,120,947 discloses examples where xanthine derivatives with the carbomethoxy substituent at the 7-position shows greater activity than theophylline.
U.S. Pat. No. 5,641,784 to Kufner-Muel et al. discloses 1,3-dialkyl xanthine derivatives that may comprise an N-linked saturated 5- or 6-membered ring which may optionally contain oxygen or sulfur as a further heteroatom. The xanthine compounds are disclosed as being useful for the symptomatic therapy of degenerative disorders of the central nervous system such as, for example, senile dementia and Alzheimer""s disease, Parkinson""s disease, and traumatic brain injury.
U.S. Pat. No. 4,696,932 to Jacobson et al. discloses xanthine derivatives characterized by the presence of lower alkyl groups such as n-propyl groups at the 1 and 3 position on the theophylline ring and by a variety of para-substituents on a 8-phenyl ring. The compounds are disclosed as having significant activity as antiallergenic and antiasthmatic drugs as well as being useful in the treatment of cardiac and renal failure, high blood pressure, and depression.
Jacobson et al., Drug Rev Res 47:45-53 (1999) discloses 8-alkyl or 8-cycloalkyl xanthine derivatives that are described as being antagonists of A2B adenosine receptors. Jacobson et al. further disclose that the A2B AR subtype has been found to be involved in the control of cell growth and gene expression, vasodilatation, and fluid secretion from intestinal epithelia.
U.S. Pat. No. 5,877,180 to Linden et al. discloses xanthine derivative antagonists of A2 adenosine receptors as being effective for the treatment of inflammatory diseases. Linden et al. further disclose that examples of the inflammatory diseases that may be treated according to U.S. Pat. No. 5,877,180 include ischemia, arthritis, asthma, multiple sclerosis, sepsis, septic shock, endotoxic shock, gram negative shock, toxic shock, hemorrhagic shock, adult respiratory distress syndrome, TNF-enhanced HIV replication and TNF inhibition of AZT and DDI activity, organ transplant rejection (including bone marrow, kidney, liver, lung, heart, skin rejection), cachexia secondary to cancer, HIV, and other infections, osteoporosis, infertility from endometriosis, cerebral malaria, bacterial meningitis, adverse effects from amphotericin B treatment, adverse effects from interleukin-2 treatment, adverse effects from OKT3 treatment, and adverse effects from GM-CSF treatment.
U.S. Pat. Nos. 5,670,498 and 5,703,085 to Suzuki et al., discloses xanthine derivative A2 receptor antagonists useful as therapeutic agents for various kinds of diseases caused by hyperergasia of adenosine A2 receptors, for example, therapeutic agents for Parkinson""s disease, anti-dementia agents, anti-depressants, anti-asthmatic agents and therapeutic agents for osteoporosis.
U.S. Pat. No. 5,516,894 to Reppert discloses A2B antagonists that are useful as therapeutics to reduce inflammatory gastrointestinal tract diseases or asthma.
An object of the present invention is to provide a method for inhibiting activation of the A2B receptor by treating the receptor with a compound of the formula: 
wherein R is an aliphatic or cycloaliphatic amine group. Preferably R is a C1 to C6 alkyl amine group, C1 to C6 dialkyl amine group, piperidino group, piperazino group, pyrrolino group, pyrrolidino group, a morpholino group, or an amino cyclohexyl derivative. More preferably, 
R is pyrrolidino as shown in the following formula:
It is another object of the present invention to provide a method of preventing and/or treating asthma, bronchospastic and allergic diseases as well as other obstructive airway-type diseases comprising administering a compound of the above-described formula (I). It is a further object of the present invention to provide a method for preventing and/or treating cardiac disease and Parkinson""s disease comprising administering a compound of formula (I).
Other objects of the present invention include a method of antagonizing A2B receptors comprising administering to a mammal in need thereof an effective amount of a compound of formula (I); a method of treating asthma comprising administering to a mammal in need thereof an effective amount of a compound of claim 1; method of treating diarrhea comprising administering to a mammal in need thereof an effective amount of a compound of formula (I).
Furthermore, the present invention discloses a method of regulating at least one of smooth muscle tone, cell growth, intestinal function, and neurosecretion.
Another object of the present invention is to provide a method of treating inflammatory gastrointestinal tract disorders comprising administering to a mammal in need thereof an effective amount of a compound of formula (I).
Another object of the present invention is to provide for a method of treating Alzheimer""s disease, Parkinson""s disease, dementia, depression, or traumatic brain injury comprising administering to a mammal in need thereof an effective amount of compound of formula (I).
Another object of the present invention is to provide a method of treating inflammatory diseases comprising administering to a mammal in need thereof an effective amount of a compound of formula (I). The inflammatory diseases include asthma, multiple sclerosis, sepsis, septic shock, endotoxic shock, gram negative shock, toxic shock, hemorrhagic shock, adult respiratory disease syndrome, TNF-enhanced HIV replication, TNF inhibition of AZT and DDI activity, organ transplant rejection, cachexia secondary to cancer, HIV, osteoporosis, infertility from endometriosis, cerebral malaria, bacterial meningitis, adverse effects from amphotericin B treatment, adverse effects from interleukin-2 treatment, adverse effects from OKT3 treatment, and adverse effects from GM-CSF treatment.
The administration of a compound of formula (I) may be, for example, by oral, parenteral, or by inhalation mans in the form of tablets, capsules, solutions, elixirs, emulsions, aerosols, and the like. Typical effective doses in humans may range from, for example, from 0.2 to 10 milligrams per kilogram of body weight, preferably from 0.4 to 5 milligrams per kilogram, more preferably from 0.6 to 2 milligrams per kilogram, depending on the route of administration. However, the effective dose can be determined by one of ordinary skill in the art without undue experimentation.